1. Field of the Invention
The present invention relates to a decoding method and apparatus, and more particularly, to a method and apparatus for correcting an error of an error correcting code (ECC) block read from an information storage medium.
2. Description of the Related Art
Data such as an image or sound is stored in discs such as compact discs (CDs) or digital versatile discs (DVDs) which are information storage media. A pickup provided in a reproducing apparatus emits a laser beam to a disc and receives the laser beam reflected from the disc to read data stored in the disc.
During operation and use, optical discs are easily scratched, or contaminant such as dust easily sticks to the surface of the optical discs. Accordingly, a probability of error burst is high when data is read from an optical disc. To overcome this problem, during recording, data is encoded into ECC blocks so that errors which may occur while the data is read can be corrected.
A reproducing apparatus performs error correction on ECC blocks read from the disc on row/column code words. Row/column code words on which an error occurs are indicated by error flags, and then error correction is performed on column/row code words based on the error flags.
In a case of a DVD, in which the length of a row code word is 182 bytes, including 10 bytes of parity, if errors occur in more than 6 bytes from the 182 bytes of the row code word, a decoder of a reproducing apparatus indicates the row code word in an error flag. Error correction on a column code word is performed based on the error flag resulting from the error correction on the row code word. When error correction is performed on the column code word, errors are deemed to have occurred in all bytes of the row indicated in the error flag. Since the error flag is generated only if errors occur in more than 6 bytes among the 182 bytes, a number of bytes that are normally read without errors is generally greater than a number of bytes having errors. However, when error correction is performed on the column code word, all of the 182 bytes of the row code word indicated in the error flag are considered to have errors. Accordingly, even if a code word is actually correctable, it is deemed that the code word cannot be corrected, thus decreasing error correction efficiency.